1. Field of the Invention
The present invention relates to an audio signal amplification and distribution system for multiple speaker applications, and, in particular, to a new and improved wall-mounted xe2x80x9cpoweredxe2x80x9d volume control having an integrated audio power amplifier for connecting between a signal source and one or more remote speakers.
2. Description of the Related Art
Broadcasting audio or music, such as background music, within a facility is generally desirable to provide a relaxing or entertaining atmosphere or to enhance a desired theme or mood. In particular, buildings such as houses, hotels, restaurants, casinos, shopping malls, and other indoor or outdoor areas often are equipped with sound distribution systems to provide music and paging capability to different locations in or around the building or area.
One simple way to provide a distributed audio sound system is to provide a number of individual signal sources and amplifiers throughout the building or area. While such a sound system may be acceptable for distributing AM or FM radio broadcasts, it would typically not be suitable for rebroadcast of an audio recording or public address message since the music or sound may not be synchronized from room-to-room. Also such sound systems necessitate multiple signal sources which can increase the costs of the system significantly, particularly if high fidelity sound reproduction is desired. For these reasons, it is generally preferred to use a single high-fidelity signal source.
A typical commercial high-fidelity sound distribution system provides for a single signal source and amplifier to provide a signal to a plurality of speakers distributed throughout a building or area. Systems of this nature advantageously provide synchronized music or paging capability to multiple areas of a building or facility. However, such systems have certain undesirable limitations or disadvantages. One disadvantage is the reduced impedance to the amplifier created by having a plurality of speakers connected to a single amplifier. Connecting too low an impedance (i.e., too many speakers) to an amplifier can overload and possibly damage the amplifier. Another disadvantage is that in large buildings a number of the speakers may be located great distances (e.g., over 100 feet) from the amplifier. Speaker wire has electrical properties of resistance, capacitance and reactance, all of which can impede or alter the transmitted audio signal, thereby causing poor audio output. This is especially true when low voltage or high-current signals are transmitted over great distances of wire.
Another limitation of traditional single amplifier systems is that the amplifier must be able to produce adequate power to operate a plurality of speakers. For large installations, the required high power amplifiers can be particularly expensive because larger and more expensive components must be used to produce the significant amounts of electrical power required. Also, the number of speakers available will be limited by the maximum power output of the central amplifier, making further expansion of the system difficult.
Another disadvantage of traditional single amplifier systems is that each speaker will produce music or a page at approximately the same volume. This may be undesirable in many applications where different audio levels may be required for different areas of a building or facility. For example, a lounge or bar area in a hotel may require music at a higher volume than in the lobby or dining areas. Thus, in such systems it is desirable to provide a means for independently adjusting the volume in each area to compensate for ambient background noise or to set a particular mood or tone suitable for each particular area.
Over the years, various devices have been proposed to provide for localized volume control. One early proposed solution was to provide a multichannel amplifier. A multichannel amplifier has a number of different channels, each having a separate volume control, and which may be used to individually control or adjust the signal strength or power provided to each speaker pair or each speaker in a single channel system. However, multichannel amplifiers are quite costly and the installer or owner is still limited in the number of speakers that the system may operate by the number of channels available on the amplifier and the maximum power output for each channel. Also, the volume control is usually located on the amplifier itself, making localized adjustment of remote speakers inconvenient. Furthermore, using a multichannel amplifier necessitates running wire between each speaker and the amplifier.
A more widely accepted solution is to provide an adjustable autoformer in series with each local speaker pair to selectively attenuate the audio signal provided to the local speakers. For example, U.S. Pat. No. 4,809,339 to Shin et al. describes one type of autoformer suitable for localized audio signal attenuation. Such autoformers typically comprise a plurality of user selectable transformer coils connected between the central amplifier and the local speaker pair. Depending upon the position of a switch or selector knob, more or less reactance and/or resistance is placed in series with the speaker pair to limit or attenuate the amount of power delivered, accordingly.
Although such autoformers provide limited localized volume adjustment of remote speakers they suffer from a number of disadvantages which have yet to be overcome by any known prior art systems. In particular, autoformer volume controls are often inconvenient in that volume control is not continuous. In other words, the volume may only be set at one of several (usually 8 to 12) discrete levels. Thus, a desired volume level located between two autoformer steps may not be achieved. Such volume controls are also undesirable where high-quality or high-fidelity audio sound output is desired. Autoformers have significant reactance to diminish the power delivered to the speakers. Passing an audio signal through an autoformer undesirably distorts the audio signal by introducing capacitance, resistance, and phase distortion at various frequencies in the audio range. In particular, the high and low frequencies of the audio signal are lost or greatly diminished when the signal passes through a transformer. Also, when several autoformers are connected together on a given output channel, the adjustment of one volume control will often result in a change of volume in an adjacent area due to the change in overall load reactance. Thus, such volume controls are not completely independently adjustable.
Other volume controls are known which suffer from similar or other drawbacks. For example, variable resistive ladders, also commonly known as an xe2x80x9cL-padxe2x80x9d or rheostat, have also been used to control the volume of the audio from one or more local speaker pairs. The resistive ladder allows the user to selectively increase or decrease the resistance in the line between the speaker and the amplifier to attenuate the audio signal. However, variable resistive ladders suffer from the additional drawback of undesirably generating significant heat and, thus, are not efficient and require extensive cooling or other heat dissipating means.
It is also known to incorporate amplifier/power boosters in a speaker itself. For example, U.S. Pat. No. 4,991,221 to Rush describes an amplifier and a speaker in a single enclosure. However, these types of systems are not well-suited for retrofit installations because the amplifier circuit requires a separate power supply line in addition to the speaker signal lines. Also, the signal quality for speaker/amplifier pairs located at extended distances from the original audio source will still suffer significant degradation due to the resistance, capacitance and inductance of the speaker wire and the relatively low signal input impedance of the amplifier/booster circuit (typically on the order of 100 Ohms). Furthermore, the gain control for such amplifier/booster circuits is typically located behind the speaker housing. This is undesirable for the vast majority of commercial and residential applications in which the speakers are typically located in inaccessible places such as on ceilings or walls out of reach.
A need exists, therefore, for a high-quality audio system for remote, multi-speaker operation which provides the capability for local continuous volume adjustment without significant signal degradation in a convenient inexpensive retrofittable system.
The present invention generally provides a simple, cost efficient, high-fidelity audio distribution system and method for providing a high-quality audio signal to numerous areas or rooms within a building or other facility. The present invention further provides the capability for users to make localized and continuous volume adjustment of remote speakers without significant noise or signal distortion. The system generally comprises one or more amplifiers and/or signal conditioners located at or near the audio source for receiving a signal from the audio source and generating an amplified audio signal which is transmitted over extended distances to one or more xe2x80x9cpoweredxe2x80x9d volume controls. Each volume control receives the amplified (low current, low resistance) signal from the amplifier and/or signal conditioner using a high-impedance input/attentuator. Desirably, this avoids unduly loading the amplifier and/or signal conditioner. Each volume control then amplifies the attenuated signal to a level determined by a user controlled adjustment device such as a variable resistor or potentiometer. Speakers are connected to the signal outputs of each volume control and receive the amplified audio signal to reproduce the music or page at the desired amplified volume level.
In accordance with one preferred embodiment the present invention comprises a powered volume control for connecting between an audio source and one or more remote speakers. An input circuit receives an audio signal from the audio source and provides a preamplified signal output. This signal is amplified by an amplifier circuit to provide an amplified signal output which is a substantial replication of the preamplified signal and the audio signal from the audio source. For the purposes of the present application, the term xe2x80x9creplicationxe2x80x9d means a generally identical version (notwithstanding distortion introduced from the circuitry) of the original signal but which may be scaled up or down in amplitude due to the attenuator or amplifier. Accordingly, the replication may be identical to, of greater magnitude, or of lesser magnitude than the original signal. It is further contemplated that the replicated signal may comprise a digitized version of the original signal.
The amplified signal output is then used to drive one or more remote speakers. To allow volume control of the remote speakers a variable adjustment device is provided. This can be adjusted by a user to change the magnitude of the preamplified signal and/or the gain or bias of the amplifier circuit such that the amplified signal output can be continuously adjusted over a predetermined range to adjust the volume of the one or more remote speakers. Advantageously, the circuitry is configured to eliminate interference, particularly in the low frequency range, from adjacent AC power sources or other sources of interference by grounding the output terminal or connector.
In accordance with another preferred embodiment the present invention comprises a wall-mounted volume control for connecting between an amplified audio signal source and one or more remote speakers. An input circuit having a relatively high input signal impedance is adapted to receive a first amplified audio signal from the amplified audio signal source to produce an attenuated audio signal having a predetermined magnitude or range of magnitudes. An amplifier circuit receives the attenuated signal and provides a second amplified signal output which is a substantial replication of the attenuated signal and the first amplified signal from the amplified audio signal source. The amplified signal is then used to drive one or more remote speakers. To adjust the volume of the speakers a variable adjustment device is provided which allows a user to adjust the magnitude of the second amplified signal such that speaker volume can be adjusted over a predetermined range.
In accordance with another preferred embodiment the present invention comprises an audio distribution system for distributing an audio signal from one or more audio sources to one or more speakers located remotely from the audio sources. A first amplifier is provided and is adapted to be located at or near the one or more audio signal sources for receiving an audio signal input from said one or more audio signal sources. The first amplifier provides a first amplified signal output which is substantially a replication of the audio signal input. A second amplifier is also provided and is adapted to be located in an accessible location on a wall remotely from the one or more audio signal sources and electrically connected between the first amplifier and the remote speakers. The second amplifier has a relatively high input signal impedance and a relatively low output signal impedance and is adapted to receive the first amplified audio signal from the first amplifier and to provide an intermediate attenuated audio signal having a predetermined magnitude or range of magnitudes. The second amplifier is further adapted to amplify the attenuated audio signal to provide a second amplified signal to drive the one or more remote speakers. The second amplified signal is a substantial replication of the attenuated audio signal and the first amplified signal. A variable adjustment device is further provided for allowing a user to adjust the magnitude of the second amplified signal whereby the volume of the one or more remote speakers can be adjusted over a predetermined range.
In accordance with another preferred embodiment the present invention comprises a method for distributing an audio signal from one or more audio sources to one or more speakers located remotely from the audio sources. According to the method the audio signal input from one or more audio signal sources is amplified to provide a first amplified signal output which is substantially a replication of the audio signal input. The first amplified signal has an amplitude or magnitude such that it is relatively impervious to spurious noise. The first amplified signal is then transmitted through an elongated electrical conductor to one or more remote locations near one or more remote speakers. The first amplified signal is then passed through a variable resistor to produce an attenuated audio signal having a desired amplitude or magnitude as determined by a user variable adjustment device. The attenuated signal is then amplified to provide a second amplified signal which is transmitting along one or more electrical conductors to drive the one or more remote speakers. The method allows for localized speaker volume control of remote speakers with less noise interference and distortion than methods utilizing conventional autoformer volume controls.
These and other embodiments of the present invention will be readily apparent to those skilled in the art having reference to the detailed description and drawings which follow, the invention not being limited, however, to any particular embodiments disclosed.